WO2018043781A1

WO2018043781A1 - Electrolyte comprising organic active material for redox flow battery and redox flow battery using same

Info

Publication number: WO2018043781A1
Application number: PCT/KR2016/009966
Authority: WO
Inventors: 진창수; 연순화; 전명석; 신경희; 이범석; 박세국; 박천범; 소재영
Original assignee: 한국에너지기술연구원
Priority date: 2016-08-31
Filing date: 2016-09-06
Publication date: 2018-03-08
Also published as: KR101937783B1; US20180277876A1; US10522863B2; KR20180024649A

Abstract

The present invention relates to an electrolyte comprising organic active material for a redox flow battery and a redox flow battery using the same and, more specifically, to an electrolyte method for a redox flow battery, the electrolyte being obtained by dissolving, in an aqueous solvent, an organic compound usable as a single active material in a positive electrode and a negative electrode, and to a redox flow battery using the same. The electrolyte according to the present invention is an aqueous electrolyte in which an active material is dissolved in an aqueous solvent, and thus has a low risk of fire or explosion, leading to excellent safety. In addition, the electrolyte has an advantage in that, by applying an organic compound applicable as a single active material in the positive and negative electrodes, the recovery of battery capacity can be achieved through the mixing of liquids even though the battery capacity is reduced through the penetration of the active material through a separator.

Description

Redox flow battery electrolyte comprising an organic active material and redox flow battery using the same

The present invention relates to a redox flow battery electrolyte comprising an organic active material and a redox flow battery using the same, and more particularly, an electrolyte solution for a redox flow battery in which an organic compound that can be used as a single active material in a positive electrode and a negative electrode is dissolved in a water-soluble solvent. And a redox flow battery using the same.

As energy use increases worldwide, the use of fossil fuels, an energy source, is gradually increasing. The use of fossil fuels is a global problem due to climate change and environmental pollution. As a solution to this problem, efficient power use is made possible by using renewable energy and energy storage system. We are planning.

Renewable energy is classified into solar energy, biomass, wind power, hydropower, fuel cell, coal liquefaction, gasification, marine energy, waste energy and others, not coal, oil, nuclear power and natural gas. It refers to a flowable fuel mixed with materials, but is actually an energy source that replaces petroleum. Various renewable energy has a great advantage to generate energy without polluting the environment, but the disadvantage is that the energy quality is not good due to the output fluctuation according to the geographical conditions and the natural environment. In order to solve this problem, energy storage devices that can store the remaining power and provide elasticity when needed are emerging as the most suitable means, and large-capacity long-term storage devices are in the spotlight.

Among the various types of energy storage devices, redox flow batteries oxidize redox couples and active materials that are dissolved in electrolyte, unlike conventional secondary batteries storing electrical energy in electrodes containing active materials. It is a secondary battery using a reduction reaction. Due to the characteristics of the redox flow battery, the stack responsible for the output and the electrolyte part for the capacity are separated from each other, and thus the capacity and output can be freely designed. Unlike other cells, the redox flow battery does not change the structure of the electrode itself because only the redox reaction is performed by the exchange of electrons from the electrode, and since the electrode and the active material are separated, side reaction between the two materials is prevented. It is excellent in stability and lifespan compared to other rechargeable batteries. Electrolyte, one of the key materials of redox flow batteries, is used by dissolving active materials having different oxidation states in water-soluble and non-aqueous solvents. At this time, a variety of redox flow battery is configured according to the type of active material, it is divided into aqueous and non-aqueous electrolyte according to the type of solvent. The electrolyte solution containing such an active material must have a fast reactivity and reversibility with the electrode, and in order to increase the energy density, it must have a wide potential window and high solubility. The electromotive force of the redox flow battery is determined by the difference between the standard electrode potentials E ^o of the redox couple constituting the positive and negative electrolytes. The main water-based redox couples developed so far are Fe / Cr, V / V, V / Br, Zn / Br, Zn / Ce and the like.

Meanwhile, the development of the redox flow battery began in the early 1974 for the aerospace using Fe / Cr based active materials in the US National Aeronautics and Space Administration (NASA). Fe / Cr used as an active material of the early redox flow battery has been limited in its use due to the permeation of the active material through the separator and the corrosion of the electrolyte.

Since then, many researchers have studied redox couples with excellent stability and reversible electrochemical reactions with electrodes.Vanadium redox flow cells were developed in 1980 by Maria Skyllas-Kazacos in Australia. . Vanadium has various oxidation values, so that both the positive and negative electrodes can be applied as a single material. When using vanadium, which is a single active material, the vanadium active material is permeated through the separator to recover the capacity through rebalancing even if the battery capacity decreases. It has a big advantage. However, the water-soluble vanadium active material has a disadvantage of low energy density due to low voltage and solubility. If the concentration of the vanadium active material is increased to increase the energy density, vanadium precipitation occurs at the cathodes V (II, III) at low temperatures below 0 ° C, and vanadium pentoxide (V ₂ O ₅ ) Precipitates. When precipitates occur in the flow battery system, the flow of the electrolyte is interrupted to increase the internal pressure of the stack, and leakage occurs, and the battery capacity is reduced by the vanadium precipitates. In addition, the vanadium used as the active material of the flow battery has a large price fluctuation according to the export volume as China accounts for 40% of the world's reserves, and the patent technology for the vanadium active material and the flow battery using the same is restricted in its use. This follows.

[Patent Document] Republic of Korea Patent Publication No. 10-2014-0016298

The present invention provides a redox flow battery electrolyte comprising an organic active material having high solubility and potential and a redox flow battery using the same.

In order to achieve the above object, the present invention comprises a supporting electrolyte, an aqueous solvent and an organic active material, the organic active material is alkyl viologene dihalide, 4,4-bipyridine ), Pyrazine (pyrazine) and quinoxaline (quinoxaline) provides an electrolyte solution for a redox flow battery, characterized in that it comprises one or more selected from the group consisting of.

The organic active material may be an active material that can use a single positive electrode and a negative electrode.

The alkyl group of the alkyl viologen dihalide may be selected from the group consisting of ethyl, methyl, propyl, butyl, heptyl and diheptyl, but is not limited thereto.

The alkyl viologen dihalide may be an alkyl viologen diiodide or an alkyl viologen diperchlorate. More preferably, it may be ethyl viologene diiodide or ethyl viologene diperchlorate.

The organic active material may be present in an electrolyte at a concentration of 0.005 M to 0.3 M, more preferably at a concentration of 0.01 M.

The supporting electrolyte may be selected from the group consisting of H ₂ SO ₄ , Li ₂ SO ₄ , Na ₂ SO ₄ , K ₂ SO ₄ and LiCl, may be present in the electrolyte at a concentration of 0.5 M to 3 M, more preferably. Preferably at a concentration of 1 M.

Examples of the aqueous solvent include water, a hydrophilic solvent, or a mixed solvent of water and a hydrophilic solvent. Here, the hydrophilic solvent may include one or more selected from the group consisting of methanol, ethanol, methyl alcohol, isopropyl alcohol, ethylene glycol and diethylene glycol.

In addition, the present invention is a positive electrode cell comprising a positive electrode and a positive electrode electrolyte; A cathode cell comprising a cathode and a cathode electrolyte; And a separator between the anode cell and the cathode cell, wherein the cathode electrolyte and the cathode electrolyte include a supporting electrolyte, an aqueous solvent, and an organic active material, and the organic active material is an alkyl viologen dihalide. It provides a redox flow battery, characterized in that selected from the group consisting of viologene dihalide, 4,4-bipyridine, pyrazine and quinoxaline.

The separator may be an anion exchange membrane or a porous membrane.

Details of the electrolyte are as described above.

The electrolyte solution according to the present invention is an aqueous electrolyte solution in which an active material is dissolved in an aqueous solvent, and thus has a low risk of fire or explosion and is excellent in stability. In addition, by applying an organic compound applicable as a single active material to the positive electrode and the negative electrode, there is an advantage that the capacity can be recovered through the mixture even if the capacity of the battery is reduced by permeation of the active material through the separator. In addition, it is possible to reduce the cost of the active material compared to the conventional flow battery (all vanadium, Zn / Br), it is possible to improve the problems with the existing vanadium active material, such as generation of precipitates.

1 is a schematic diagram of (a) a cyclic voltammogram and (b) a three-electrode system.

FIG. 2 shows a cyclic voltammetry curve of ethyl viologen diiodide in an aqueous solvent containing various supporting electrolytes.

3 shows a cyclic voltammetry curve of Ethyl viologen diperchlorate in an aqueous solvent containing various supporting electrolytes.

4 shows a cyclic voltammetry curve of 4,4-Bipyridine in an aqueous solvent containing various supporting electrolytes.

5 shows a cyclic voltammetry curve of Pyrazine in an aqueous solvent containing various supporting electrolytes.

6 Quinoxaline's cyclic voltammograms are shown in aqueous solvents containing various supporting electrolytes.

7 is a schematic diagram schematically showing a configuration of a redox flow battery.

8 is a charge and discharge test of an Ethyl viologen diiodide redox flow battery to which a FAP-450 separator is applied, (a) when the current density is 10 mA / cm ² , (b) when 5 mA / cm ² , and (c ) It shows the potential change over time, current efficiency, energy efficiency and potential efficiency at 1 mA / cm ² , and (d) the discharge capacity, current efficiency, energy efficiency and potential efficiency according to the number of charge and discharge cycles.

9 is a charge / discharge test of an Ethyl viologen diiodide redox flow battery to which a FAP-375-PP separator is applied, (a) when the current density is 10 mA / cm ² , and (b) when 5 mA / cm ^{2 is} used. (c) shows the potential change over time, current efficiency, energy efficiency and potential efficiency at 1 mA / cm ² , and (d) results of discharge capacity, current efficiency, energy efficiency and potential efficiency according to the number of charge and discharge cycles. to be.

FIG. 10 is a charge / discharge test of a Pyrazine-NaI redox flow battery, and shows results of current capacity and potential measured according to the number of charge / discharge cycles.

[Description of the code]

110: end plate 120: carbon electrode

130: separator 140: flow frame

150: graphite plate 160: electrode current collector

Hereinafter, the present invention will be described in more detail with reference to Examples. The objects, features and advantages of the present invention will be readily understood through the following examples. The present invention is not limited to the embodiments described herein and may be embodied in other forms. The embodiments introduced herein are provided to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention should not be limited by the following examples.

실시예Example : 유기 활물질을 포함하는 : Containing an organic active material 레독스Redox 플로우Flow 전지용 전해액 제조 Manufacture of electrolyte for battery

In the electrolyte solution including the organic active material used in the present invention, an active material and a supporting electrolyte were added to an aqueous solvent to prepare an electrolyte solution. The types and concentrations of the organic active material, the supporting electrolyte, and the solvent used are shown in Table 1, and the electrochemical characteristics of the electrolyte prepared by the cyclic voltammetry and the charge / discharge test were performed.

TABLE 1

Types and Concentrations of Active Material, Supporting Electrolyte, and Solvent Used to Prepare Redox Flow Battery Electrolyte

실험예 1: 순환전압전류법에 의한 산화환원 반응 확인Experimental Example 1: Confirmation of redox reaction by cyclic voltammetry

Cyclic voltammetry (CV) was used for electrochemical characterization of the electrolyte prepared in Example. The cyclic voltammetry method is a commonly used electrochemical measurement method in which a current-potential curve is obtained by scanning a triangular wave at a constant speed through the electrode potential of the working electrode. The method of recording a current flowing in a potential-current curve when the potential is changed in proportion to time is called a potential sweep method. When the potential is repeatedly applied, it is called a cyclic voltammetry method. This is used in the electrochemical field to qualitatively grasp the reaction occurring on the surface of the electrode such as the potential at which the reaction occurs, the speed of the reaction, and the reactivity of the reaction product.

In the CV measurement, E _pa means the oxidized peak potential, E _pc means the cathodic peak potential, and E _p / 2 ((E _pa + E _pc ) / 2) is the average of both peak potentials. Indicates. In addition, I _pa means an oxidized peak current (Anodic peak current), I _pc means a reduced peak current (Cathodic peak current) (Fig. 1 (a)). In the case of reversible reactions, the magnitude of the redox current or peak current is proportional to the square of the scan rate. The higher the absolute value of E _p / 2, the higher the potential of the active material used in the redox flow battery, and the closer the ratio of the oxidation / reduction peak current value (I _pa / I _pc ) to 1, the closer to the reversible reaction.

The cyclic voltammetry used in the present invention was conducted with a three-electrode system. The electrode in which the electrode reaction to be measured is called a working electrode. In this experiment, a glass carbon electrode with a diameter of 3 mm was used, and the reference electrode was Ag / AgCl and the counter electrode. Silver platinum wire (platinum wire) was used (Fig. 1 (b)).

1-1: Ethyl viologen diiodide의 CV 측정1-1: CV Measurement of Ethyl viologen diiodide

In order to confirm the redox reaction and the standard electrode potential E ^o of ethyl viologen diiodide, each electrolyte was prepared by adding 0.01 M of Ethyl viologen diiodide and the supporting electrolytes of Table 1 and NaCl and KCl as supporting electrolytes. At this time, only K ₂ SO ₄ 0.5 M was added, the remaining support electrolyte was added 1 M concentration. Each electrode was placed in the prepared electrolyte and then connected to a potentiostat / galvanostat for cyclic voltammetry experiments. The scan rate indicative of the potential 기 phase velocity was given at 100 mV / s.

As a result, redox peaks were observed at the cathode potential and the anode potential of all the electrolyte solutions (FIG. 2). Through this, it was confirmed that the electrolyte of the present invention showed a reversible redox reaction. The difference between the oxidation / reduction peak potentials and the average value of the peak potentials are shown in Table 2.

TABLE 2

In terms of the reaction mechanism, ethyl viologen is a compound containing 4,4'-bipyridinium, and has three oxidation states of EVD ²⁺ , EVD ⁺ , and EVD ⁰ . At this time, the redox reaction of EVD ²⁺ ↔ EVD ⁺ occurs at E ₁ , and the redox potential of EVD ⁺ ↔ EVD ⁰ occurs at E ₂ .

In addition, the diiodide reaction of viologen diiodide compound showed redox reaction at the anode potential.

I ₃ ^{^-} + 2e- ↔ 3I ^-

1-2:1-2: Ethyl viologen diperchlorate의 CV 측정CV measurement of ethyl viologen diperchlorate

In order to confirm the redox reaction and the standard electrode potential E ^o of ethyl viologen diperchlorate, an electrolyte solution was prepared under the same conditions as in Experimental Example 1-1, and the experiment was performed.

As a result, Ethyl viologen diperchlorate showed a reversible redox reaction at the cathode potential, and the results are shown in FIG. The difference between the oxidation / reduction peak potentials and the average value of the peak potentials are shown in Table 3.

TABLE 3

1-3:1-3: 4,4- Bipyridine의 CV 측정CV measurement of 4,4-bipyridine

In order to confirm the redox reaction of 4,4-Bipyridine and the standard electrode potential E ^o , an electrolyte solution was prepared under the same conditions as in Experimental Example 1-1, and the experiment was performed.

As a result, 4,4-Bipyridine showed a reversible redox reaction at the cathode potential, the results are shown in FIG. The difference between the oxidation / reduction peak potentials and the average value of the peak potentials are shown in Table 4.

TABLE 4

1-4:1-4: Pyrazine의 CV 측정CV measurement of Pyrazine

In order to confirm the redox reaction of Pyrazine and the standard electrode potential E ^o , an electrolyte was prepared under the same conditions as in Experimental Example 1-1, and the experiment was performed.

As a result, Pyrazine showed a reversible redox reaction at the cathode potential, and the results are shown in FIG. 5. The difference between the oxidation / reduction peak potentials and the average value of the peak potentials are shown in Table 5.

TABLE 5

1-5:1-5: Quinoxaline의Quinoxaline CVCV 측정 Measure

In order to confirm the redox reaction and the standard electrode potential E ^o of quinoxaline, an electrolyte solution was prepared under the same conditions as in Experimental Example 1-1 and the experiment was conducted.

As a result, Quinoxaline showed a reversible redox reaction at the negative electrode potential in the electrolyte solution using the supporting electrolyte except H ₂ SO ₄ and Li ₂ SO ₄ , and the results are shown in FIG. 6. The difference between the oxidation / reduction peak potentials and the average value of the peak potentials are shown in Table 6.

TABLE 6

실험예 2: 레독스 플로우 전지의 충방전 테스트Experimental Example 2: Charge / Discharge Test of Redox Flow Battery

2-1: Ethyl viologen diiodide의 충방전 테스트2-1: Charge-Discharge Test of Ethyl viologen diiodide

A 0.2 M EVD active material was dissolved in a 1 M LiCl supporting electrolyte and an aqueous solvent to prepare an electrolyte. An electrolyte was injected into the cathode and the cathode in the same amount of 3 ml, and then a redox flow battery was manufactured in the configuration as shown in FIG. 7. It was. In this case, a carbon felt electrode (Toyobo, XF-30A, t = 4 mm) having an area of 12 cm ² was used for the anode and cathode cells, and the separator was an anion exchange membrane (Fumatech, FAP-450 (thickness). 50 μm), FAP-375-PP (thickness 70 μm)) was used. Thereafter, the battery was charged and discharged at room temperature (25 ^° C.) using a Maccor 4000 Maccor company. The charging and discharging voltage range was charged and discharged with the upper limit voltage 1.65 V and the lower limit voltage 0 V, and the current density was continuously charged and discharged at 10, 5, and 1 mA / cm ² .

Experimental results showed that the current efficiency was the highest at 96.0% when the current density was 10 mA / cm ² in the cell using the FAP-450 membrane, but the highest energy efficiency was obtained at 53.0 mA / cm ² at 63.0%. The efficiency was highest with 72.7% at 1 mA / cm ² . The discharge capacity did not deviate significantly from the 20 mAh band even though the number of charge and discharge cycles continued (FIG. 8).

On the other hand, in the battery using the FAP-375-PP separator, the current efficiency was 96.0% when the current density was 5 mA / cm ² , but the energy efficiency and the potential efficiency were 74.9% and 83.2 at 1 mA / cm ² , respectively. The highest percentage came out. The discharge capacity was similar to that of the battery using the FAP-450 separator (FIG. 9).

2-2: Pyrazine-NaI의 충방전 테스트 2-2: Charge / Discharge Test of Pyrazine-NaI

Since pyrazine showed redox reaction in the negative electrode as in Experimental Example 1-4, 0.3 M pryazine and 2 M NaCl supporting electrolyte were dissolved in an aqueous solvent and used as a negative electrode electrolyte, and 0.3 M NaI and 2 M NaCl were water-soluble. It was dissolved in a solvent and used as a positive electrolyte solution. The prepared electrolyte was injected into the electrolyte in the same amount of 3 ml each of the positive electrode and the negative electrode, and then a redox flow battery was manufactured with the configuration as shown in FIG. 8. In this case, a carbon felt electrode (Toyobo, XF-30A, t = 4 mm) having an area of 12 cm ² was used as the electrode for the anode cell and the cathode cell, and the separator was a celgard 3501 porous membrane. Thereafter, the battery was charged and discharged at room temperature (25 ^° C.) using a Maccor 4000 Maccor company. The charging and discharging voltage range was charged and discharged with an upper limit voltage of 2 V and a lower limit voltage of 0.8 V to 1.2 V. The current density was continuously charged and discharged at 40 mA / cm ² .

As a result, as the number of charge and discharge increased, the maximum capacity of the battery was reduced, but it was confirmed that the maximum potential was maintained at 2.0 V (FIG. 10).

As described above in detail specific parts of the present invention, it will be apparent to those skilled in the art that these specific descriptions are merely preferred embodiments, and thus the scope of the present invention is not limited thereto. will be. Thus, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims

A supporting electrolyte, an aqueous solvent, and an organic active material,

The organic active material includes at least one selected from the group consisting of alkyl viologene dihalide, 4,4-bipyridine, pyrazine and quinoxaline. The electrolyte solution for redox flow batteries characterized by the above-mentioned.
The method according to claim 1,

The organic active material is a redox flow battery electrolyte, characterized in that the active material that can be used as a single cathode.
The method according to claim 1,

The alkyl group of the alkyl viologen dihalide is selected from the group consisting of ethyl, methyl, propyl, butyl, heptyl and diheptyl electrolyte for redox flow battery.
The method according to claim 1,

The alkyl viologen dihalide is an alkyl viologen diiodide or an alkyl viologen diperchlorate.
The method according to claim 1,

The alkyl viologen dihalide is ethyl viologene diiodide (ethyl viologene diiodide) or ethyl viologene diperchlorate (ethyl viologene diperchlorate), characterized in that the electrolyte for redox flow battery.
The method according to claim 1,

The organic active material is a redox flow battery electrolyte, characterized in that present in a concentration of 0.005 M ~ 0.3 M in the electrolyte.
The method according to claim 1,

The supporting electrolyte is selected from the group consisting of H 2 SO 4 , Li 2 SO 4 , Na 2 SO 4 , K 2 SO 4 and LiCl electrolyte for redox flow battery.
The method according to claim 1,

The supporting electrolyte is a redox flow battery electrolyte, characterized in that present in a concentration of 0.5 M ~ 3 M.
A cathode cell comprising an anode and an anode electrolyte solution;

A cathode cell comprising a cathode and a cathode electrolyte; And

A redox flow battery comprising a separator between the positive cell and the negative cell,

The positive electrode electrolyte and the negative electrode electrolyte comprises a supporting electrolyte, an aqueous solvent and an organic active material,

The organic active material is selected from the group consisting of alkyl viologene dihalide, 4,4-bipyridine, pyrazine and quinoxaline. Redox flow battery.
The method according to claim 9,

The separator is a redox flow battery, characterized in that an anion exchange membrane or a porous membrane.